Despite new divergent plotted paths of the missing Malaysia Airlines
Boeing Co.
777-200ER, investigators and aerospace officials are gaining a better understanding of where the breadcrumbs from Flight 370 originated and where they might lead, according to two people familiar with the search.

The expansive search for the missing plane, last seen over a week ago after departing Kuala Lumpur for Beijing with 239 people aboard, has relied on technologies from underwater robots to orbiting satellites.

The search zone for Malaysia Airlines MH370 is expanding. How do planes and helicopters go about finding the missing flight. WSJ's Jason Bellini has #TheShortAnswer.

On Saturday, Malaysia's prime minister said he believed "deliberate action" caused the plane's disappearance and that the search would now focus on two new corridors: a northern one spanning an area from northern Thailand to the Kazakhstan-Turkmenistan border and a southern one spanning an area from Indonesia to the southern Indian Ocean.

"Due to the type of satellite data, we are unable to confirm the precise location of the plane when it last made contact with the satellite," said Malaysian Prime Minister
Najib Razak.
He said aviation authorities in Malaysia and their international counterparts have "determined that the plane's last communication with the satellite was in one of two possible corridors."

The twin possible paths of the errant jetliner were derived from detailed calculations using the jet's last known heading, speed and likely fuel consumption allowing investigators to determine where Flight 370 was last seen and where it might have later exhausted its fuel.

Investigative teams used a series of hourly pings sent from the
Inmarsat
PLC satellite in geostationary orbit more than 22,000 miles above to the 777 after it was last spotted at 2:15 a.m. Malaysia local time by primary radar over the Malacca Strait heading for the Andaman Sea. The plots of those pings prompted search and rescue teams to expand into massive search areas.

As a result, the northern corridor and the southern corridor reflect where the 777 might have been when it sent its final ping at 8:11 a.m. Malaysia local time, some 7½ hours after leaving the Malaysian capital.

With the search area widening and the potential cause of the vanishing jet narrowing down to the actions of someone on board the aircraft, those briefed on the inquiry gained a better understanding of the unfolding investigation during a week of little public disclosure.

Recent upgrades to the Inmarsat satellite constellation make it capable of receiving detailed position, altitude and speed data embedded in its pings to aircraft flying below. However, the 12-year-old Boeing jetliner wasn't configured to broadcast those definitive points of data, people being briefed on the investigation say, as they first believed.

Because the angle and distance of the aircraft relative to the orbiting satellite changed as the jet flew over the Earth's surface, each ping — the digital equivalent of a handshake — to Flight 370 gave Malaysian officials, the National Transportation Safety Board, the Federal Aviation Administration and the U.K.'s Air Accidents Investigation Branch enough information to plot the 777's speed, altitude and changing path.

With the data at hand, investigators were unable to determine if the jet's pings were north or south of its last known primary radar sighting. Two points on the globe below the satellite, with mirror angles and equal distances from the satellite, left investigators to conclude the jet had sent its final satellite ping in the probable corridors to the north or south.

The satellites "can't give straight directional" guidance, "therefore the calculation is looking left and right of the satellite," said an industry official briefed on the investigation. The estimated path "suffers from the fact that...the system wasn't set up for that."

Officials in government and industry have regarded the southern corridor into the Indian Ocean as the more likely path of the 777, but haven't ruled out the northern arc.

The track from northern Thailand to Kazakhstan crosses some of the most heavily militarized airspace in the world, including western China. According to the industry official, many of those nations "would have MiGs up in the sky before you even knew it" to intercept any unidentified flying object.